The present invention relates to powered woodworking tools and, more particularly, to anti-kickback devices which are incorporated into the splitters of table saws, radial arm saws, and the like.
A table saw typically consists of a substantially flat table top having a centrally-located slot, a saw motor adjustably mounted beneath the table top, and a saw blade mounted on an output spindle of the saw motor and positioned to protrude upwardly through the table slot. The motor is mounted on the table saw such that the saw blade, normally disk-shaped, rotates in a direction opposite that which the workpiece is fed into the saw blade. Most table saws include a saw fence for guiding a workpiece during ripping operations, and a miter gauge, which slides in a slot in the table orientated parallel to the saw blade, for guiding a workpiece to perform cross-cutting operations.
If the saw blade should bind in the kerf of a workpiece during a ripping or cross-cutting operation, the blade grabs the adjacent portion of the workpiece and tends to carry it along as it rotates. This rotational movement of the saw blade causes the workpiece to be kicked upwardly and rearwardly back toward the operator abruptly and with great force and speed. This occurrence, known as "kickback," may result from a number of conditions, such as the use of a dull saw blade or one with insufficient set, making a freehand cut, cross-cutting against the rip fence, releasing the workpiece before it has been fed completely past the saw blade, or cutting a defective wooden workpiece.
In order to prevent the occurrence of kickback, most table saws are fitted with splitters and with kickback fingers. A splitter is a flat plate, preferably made of steel, which projects upwardly from the saw table and lies in a common plane with, and to the rear of, the saw blade. The splitter is positioned adjacent to the saw blade and the side of the splitter immediately adjacent to the saw blade has an arcuate contour which corresponds to the curve of the periphery of the saw blade, so that the splitter extends partially about the circumference of the saw blade.
A splitter is as thick as, or is slightly thinner than the saw blade so that it fits within the kerf made by a saw blade as a workpiece is fed past it. A splitter prevents the kerf from closing around the saw blade so that the body of the saw blade is prevented from binding against the sides of the cut workpiece.
Kickback fingers typically consist of a pair of elongate pawls pivotally mounted at one end to the splitter and spring biased to extend downwardly and rearwardly toward the saw table. The pawls are attached to both sides of the splitter and include teeth formed in a lower edge. The teeth point rearwardly so that the pawls do not grip a workpiece as it is fed into the saw blade.
In such a normal feed situation, the pawls pivot upwardly and ride over the upper surface of the workpiece. However, if kickback occurs, the sudden upward and reverse movement of the workpiece causes the teeth to dig into the upper surface of the workpiece and the pawls pivot forwardly to jam the workpiece against the table, thereby preventing its reverse movement from continuing.
A disadvantage with anti-kickback systems of this type is that, under certain circumstances, the teeth of the kickback pawls do not engage a workpiece in a kickback situation. This may occur when cutting plastics or wood laminates which have smooth, relatively hard upper surfaces which cannot be easily gripped by the teeth of the pawls. Another situation occurs when a relatively thick workpiece is used which causes the pawls to pivot upwardly sufficiently that the teeth are orientated at an angle which makes it difficult to engage the upper surface of the workpiece.
Accordingly, there is a need for an anti-kickback system which can accommodate workpieces made of plastic and wood laminates as well as wood, and can accommodate workpieces having varying thicknesses. Furthermore, there is a need for an anti-kickback system in which the workpiece is not damaged by teeth or other gripping means if a kickback situation occurs.